Clean room environments in which ceiling grids containing filter panels are employed are well known in the art. Such systems generally employ dropped ceilings above which is a plenum from which air passes through the filter panels in the ceiling grid into the clean room. Normally, in a clean room environment, it is imperative to achieve a hermetic seal for the filter panels in the ceiling grid since the particulate count in the room must normally be maintained at 10 particulates per cubic foot or less even though the air above the plenum often contains as many as 100,000 particulates, even under ideal conditions. In an attempt to provide such a hermetic seal so that no air can leak around the filter panels where they contact the supporting ceiling grid, prior art techniques have employed the mounting of filter panels in troughs filled with a Vaseline like substance in an effort to provide a hermetic type seal while allowing the filter panel to be readily removed for access or replacement. Such an arrangement has proved both costly and messy. Moreover, although the use of magnetic sealing fluids is known with respect to high speed rotating shafts, such a fluid, such as Ferrofluid, which is a commercially available collodial suspension of ferric oxide, has not been employed in connection with ceiling grids nor with such grids in a clean room environment. Prior art sealing techniques which have been employed to prevent particulate migration have not proved satisfactory from applicants' point of view. These disadvantages of the prior art are overcome by the present invention.